<!DOCTYPE html>
<html lang="en-us">
  <head>

    <meta http-equiv="content-type" content="text/html; charset=utf-8">
    
<meta charset="UTF-8">
<title>Reverse nested Aggregation | Elasticsearch Guide [7.7] | Elastic</title>
<link rel="home" href="index.html" title="Elasticsearch Guide [7.7]">
<link rel="up" href="search-aggregations-bucket.html" title="Bucket Aggregations">
<link rel="prev" href="search-aggregations-bucket-rare-terms-aggregation.html" title="Rare Terms Aggregation">
<link rel="next" href="search-aggregations-bucket-sampler-aggregation.html" title="Sampler Aggregation">
<meta name="DC.type" content="Learn/Docs/Elasticsearch/Reference/7.7">
<meta name="DC.subject" content="Elasticsearch">
<meta name="DC.identifier" content="7.7">
<meta name="robots" content="noindex,nofollow">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <script src="https://cdn.optimizely.com/js/18132920325.js"></script>
    <link rel="apple-touch-icon" sizes="57x57" href="/apple-icon-57x57.png">
    <link rel="apple-touch-icon" sizes="60x60" href="/apple-icon-60x60.png">
    <link rel="apple-touch-icon" sizes="72x72" href="/apple-icon-72x72.png">
    <link rel="apple-touch-icon" sizes="76x76" href="/apple-icon-76x76.png">
    <link rel="apple-touch-icon" sizes="114x114" href="/apple-icon-114x114.png">
    <link rel="apple-touch-icon" sizes="120x120" href="/apple-icon-120x120.png">
    <link rel="apple-touch-icon" sizes="144x144" href="/apple-icon-144x144.png">
    <link rel="apple-touch-icon" sizes="152x152" href="/apple-icon-152x152.png">
    <link rel="apple-touch-icon" sizes="180x180" href="/apple-icon-180x180.png">
    <link rel="icon" type="image/png" href="/favicon-32x32.png" sizes="32x32">
    <link rel="icon" type="image/png" href="/android-chrome-192x192.png" sizes="192x192">
    <link rel="icon" type="image/png" href="/favicon-96x96.png" sizes="96x96">
    <link rel="icon" type="image/png" href="/favicon-16x16.png" sizes="16x16">
    <link rel="manifest" href="/manifest.json">
    <meta name="apple-mobile-web-app-title" content="Elastic">
    <meta name="application-name" content="Elastic">
    <meta name="msapplication-TileColor" content="#ffffff">
    <meta name="msapplication-TileImage" content="/mstile-144x144.png">
    <meta name="theme-color" content="#ffffff">
    <meta name="naver-site-verification" content="936882c1853b701b3cef3721758d80535413dbfd">
    <meta name="yandex-verification" content="d8a47e95d0972434">
    <meta name="localized" content="true">
    <meta name="st:robots" content="follow,index">
    <meta property="og:image" content="https://www.elastic.co/static/images/elastic-logo-200.png">
    <link rel="shortcut icon" href="/favicon.ico" type="image/x-icon">
    <link rel="icon" href="/favicon.ico" type="image/x-icon">
    <link rel="apple-touch-icon-precomposed" sizes="64x64" href="/favicon_64x64_16bit.png">
    <link rel="apple-touch-icon-precomposed" sizes="32x32" href="/favicon_32x32.png">
    <link rel="apple-touch-icon-precomposed" sizes="16x16" href="/favicon_16x16.png">
    <!-- Give IE8 a fighting chance -->
    <!--[if lt IE 9]>
    <script src="https://oss.maxcdn.com/html5shiv/3.7.2/html5shiv.min.js"></script>
    <script src="https://oss.maxcdn.com/respond/1.4.2/respond.min.js"></script>
    <![endif]-->
    <link rel="stylesheet" type="text/css" href="/guide/static/styles.css">
  </head>

  <!--© 2015-2021 Elasticsearch B.V. Copying, publishing and/or distributing without written permission is strictly prohibited.-->

  <body>
    <!-- Google Tag Manager -->
    <script>dataLayer = [];</script><noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-58RLH5" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
    <script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start': new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0], j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src= '//www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f); })(window,document,'script','dataLayer','GTM-58RLH5');</script>
    <!-- End Google Tag Manager -->

    <!-- Global site tag (gtag.js) - Google Analytics -->
    <script async src="https://www.googletagmanager.com/gtag/js?id=UA-12395217-16"></script>
    <script>
      window.dataLayer = window.dataLayer || [];
      function gtag(){dataLayer.push(arguments);}
      gtag('js', new Date());
      gtag('config', 'UA-12395217-16');
    </script>

    <!--BEGIN QUALTRICS WEBSITE FEEDBACK SNIPPET-->
    <script type="text/javascript">
      (function(){var g=function(e,h,f,g){
      this.get=function(a){for(var a=a+"=",c=document.cookie.split(";"),b=0,e=c.length;b<e;b++){for(var d=c[b];" "==d.charAt(0);)d=d.substring(1,d.length);if(0==d.indexOf(a))return d.substring(a.length,d.length)}return null};
      this.set=function(a,c){var b="",b=new Date;b.setTime(b.getTime()+6048E5);b="; expires="+b.toGMTString();document.cookie=a+"="+c+b+"; path=/; "};
      this.check=function(){var a=this.get(f);if(a)a=a.split(":");else if(100!=e)"v"==h&&(e=Math.random()>=e/100?0:100),a=[h,e,0],this.set(f,a.join(":"));else return!0;var c=a[1];if(100==c)return!0;switch(a[0]){case "v":return!1;case "r":return c=a[2]%Math.floor(100/c),a[2]++,this.set(f,a.join(":")),!c}return!0};
      this.go=function(){if(this.check()){var a=document.createElement("script");a.type="text/javascript";a.src=g;document.body&&document.body.appendChild(a)}};
      this.start=function(){var a=this;window.addEventListener?window.addEventListener("load",function(){a.go()},!1):window.attachEvent&&window.attachEvent("onload",function(){a.go()})}};
      try{(new g(100,"r","QSI_S_ZN_emkP0oSe9Qrn7kF","https://znemkp0ose9qrn7kf-elastic.siteintercept.qualtrics.com/WRSiteInterceptEngine/?Q_ZID=ZN_emkP0oSe9Qrn7kF")).start()}catch(i){}})();
    </script><div id="ZN_emkP0oSe9Qrn7kF"><!--DO NOT REMOVE-CONTENTS PLACED HERE--></div>
    <!--END WEBSITE FEEDBACK SNIPPET-->

    <div id="elastic-nav" style="display:none;"></div>
    <script src="https://www.elastic.co/elastic-nav.js"></script>

    <!-- Subnav -->
    <div>
      <div>
        <div class="tertiary-nav d-none d-md-block">
          <div class="container">
            <div class="p-t-b-15 d-flex justify-content-between nav-container">
              <div class="breadcrum-wrapper"><span><a href="/guide/" style="font-size: 14px; font-weight: 600; color: #000;">Docs</a></span></div>
            </div>
          </div>
        </div>
      </div>
    </div>

    <div class="main-container">
      <section id="content">
        <div class="content-wrapper">

          <section id="guide" lang="en">
            <div class="container">
              <div class="row">
                <div class="col-xs-12 col-sm-8 col-md-8 guide-section">
                  <!-- start body -->
                  <div class="page_header">
<strong>IMPORTANT</strong>: No additional bug fixes or documentation updates
will be released for this version. For the latest information, see the
<a href="../current/index.html">current release documentation</a>.
</div>
<div id="content">
<div class="breadcrumbs">
<span class="breadcrumb-link"><a href="index.html">Elasticsearch Guide [7.7]</a></span>
»
<span class="breadcrumb-link"><a href="search-aggregations.html">Aggregations</a></span>
»
<span class="breadcrumb-link"><a href="search-aggregations-bucket.html">Bucket Aggregations</a></span>
»
<span class="breadcrumb-node">Reverse nested Aggregation</span>
</div>
<div class="navheader">
<span class="prev">
<a href="search-aggregations-bucket-rare-terms-aggregation.html">« Rare Terms Aggregation</a>
</span>
<span class="next">
<a href="search-aggregations-bucket-sampler-aggregation.html">Sampler Aggregation »</a>
</span>
</div>
<div class="section">
<div class="titlepage"><div><div>
<h2 class="title">
<a id="search-aggregations-bucket-reverse-nested-aggregation"></a>Reverse nested Aggregation<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/aggregations/bucket/reverse-nested-aggregation.asciidoc">edit</a>
</h2>
</div></div></div>
<p>A special single bucket aggregation that enables aggregating on parent docs from nested documents. Effectively this
aggregation can break out of the nested block structure and link to other nested structures or the root document,
which allows nesting other aggregations that aren’t part of the nested object in a nested aggregation.</p>
<p>The <code class="literal">reverse_nested</code> aggregation must be defined inside a <code class="literal">nested</code> aggregation.</p>
<div class="ulist itemizedlist">
<p class="title"><strong>Options:</strong></p>
<ul class="itemizedlist">
<li class="listitem">
<code class="literal">path</code> - Which defines to what nested object field should be joined back. The default is empty,
which means that it joins back to the root / main document level. The path cannot contain a reference to
a nested object field that falls outside the <code class="literal">nested</code> aggregation’s nested structure a <code class="literal">reverse_nested</code> is in.
</li>
</ul>
</div>
<p>For example, lets say we have an index for a ticket system with issues and comments. The comments are inlined into
the issue documents as nested documents. The mapping could look like:</p>
<div class="pre_wrapper lang-console">
<pre class="programlisting prettyprint lang-console">PUT /issues
{
    "mappings": {
         "properties" : {
             "tags" : { "type" : "keyword" },
             "comments" : { <a id="CO238-1"></a><i class="conum" data-value="1"></i>
                 "type" : "nested",
                 "properties" : {
                     "username" : { "type" : "keyword" },
                     "comment" : { "type" : "text" }
                 }
             }
         }
    }
}</pre>
</div>
<div class="console_widget" data-snippet="snippets/507.console"></div>
<div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO238-1"><i class="conum" data-value="1"></i></a></p>
</td>
<td align="left" valign="top">
<p>The <code class="literal">comments</code> is an array that holds nested documents under the <code class="literal">issue</code> object.</p>
</td>
</tr>
</table>
</div>
<p>The following aggregations will return the top commenters' username that have commented and per top commenter the top
tags of the issues the user has commented on:</p>
<div class="pre_wrapper lang-console">
<pre class="programlisting prettyprint lang-console">GET /issues/_search
{
  "query": {
    "match_all": {}
  },
  "aggs": {
    "comments": {
      "nested": {
        "path": "comments"
      },
      "aggs": {
        "top_usernames": {
          "terms": {
            "field": "comments.username"
          },
          "aggs": {
            "comment_to_issue": {
              "reverse_nested": {}, <a id="CO239-1"></a><i class="conum" data-value="1"></i>
              "aggs": {
                "top_tags_per_comment": {
                  "terms": {
                    "field": "tags"
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}</pre>
</div>
<div class="console_widget" data-snippet="snippets/508.console"></div>
<p>As you can see above, the <code class="literal">reverse_nested</code> aggregation is put in to a <code class="literal">nested</code> aggregation as this is the only place
in the dsl where the <code class="literal">reverse_nested</code> aggregation can be used. Its sole purpose is to join back to a parent doc higher
up in the nested structure.</p>
<div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO239-1"><i class="conum" data-value="1"></i></a></p>
</td>
<td align="left" valign="top">
<p>A <code class="literal">reverse_nested</code> aggregation that joins back to the root / main document level, because no <code class="literal">path</code> has been defined.
Via the <code class="literal">path</code> option the <code class="literal">reverse_nested</code> aggregation can join back to a different level, if multiple layered nested
object types have been defined in the mapping</p>
</td>
</tr>
</table>
</div>
<p>Possible response snippet:</p>
<div class="pre_wrapper lang-console-result">
<pre class="programlisting prettyprint lang-console-result">{
  "aggregations": {
    "comments": {
      "doc_count": 1,
      "top_usernames": {
        "doc_count_error_upper_bound" : 0,
        "sum_other_doc_count" : 0,
        "buckets": [
          {
            "key": "username_1",
            "doc_count": 1,
            "comment_to_issue": {
              "doc_count": 1,
              "top_tags_per_comment": {
                "doc_count_error_upper_bound" : 0,
                "sum_other_doc_count" : 0,
                "buckets": [
                  {
                    "key": "tag_1",
                    "doc_count": 1
                  }
                  ...
                ]
              }
            }
          }
          ...
        ]
      }
    }
  }
}</pre>
</div>
</div>
<div class="navfooter">
<span class="prev">
<a href="search-aggregations-bucket-rare-terms-aggregation.html">« Rare Terms Aggregation</a>
</span>
<span class="next">
<a href="search-aggregations-bucket-sampler-aggregation.html">Sampler Aggregation »</a>
</span>
</div>
</div>

                  <!-- end body -->
                </div>
                <div class="col-xs-12 col-sm-4 col-md-4" id="right_col">
                  <div id="rtpcontainer" style="display: block;">
                    <div class="mktg-promo">
                      <h3>Most Popular</h3>
                      <ul class="icons">
                        <li class="icon-elasticsearch-white"><a href="https://www.elastic.co/webinars/getting-started-elasticsearch?baymax=default&amp;elektra=docs&amp;storm=top-video">Get Started with Elasticsearch: Video</a></li>
                        <li class="icon-kibana-white"><a href="https://www.elastic.co/webinars/getting-started-kibana?baymax=default&amp;elektra=docs&amp;storm=top-video">Intro to Kibana: Video</a></li>
                        <li class="icon-logstash-white"><a href="https://www.elastic.co/webinars/introduction-elk-stack?baymax=default&amp;elektra=docs&amp;storm=top-video">ELK for Logs &amp; Metrics: Video</a></li>
                      </ul>
                    </div>
                  </div>
                </div>
              </div>
            </div>
          </section>

        </div>


<div id="elastic-footer"></div>
<script src="https://www.elastic.co/elastic-footer.js"></script>
<!-- Footer Section end-->

      </section>
    </div>

<script src="/guide/static/jquery.js"></script>
<script type="text/javascript" src="/guide/static/docs.js"></script>
<script type="text/javascript">
  window.initial_state = {}</script>
  </body>
</html>
